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Mathematics 7 Online
OpenStudy (marcelie):

Help please find the derrative

OpenStudy (marcelie):

cot inverse ( t) + cot inverse ( 1/t)

OpenStudy (marcelie):

anyone can help me

OpenStudy (jdoe0001):

hold the mayo

OpenStudy (marcelie):

@Directrix

OpenStudy (marcelie):

im so lost about this ..

OpenStudy (jdoe0001):

hmmm one sec... not one I had offhand =) but \(\cfrac{d}{dx}[cot^{-1}(x)]=-\cfrac{1}{1+x^2}\qquad thus \\ \quad \\ cot^{-1}(t)+cot^{-1}\left( \frac{1}{t} \right)\implies cot^{-1}(t)+cot^{-1}\left( t^{-1} \right) \\ \quad \\ -\cfrac{1}{1+t^2}-\cfrac{1}{1+t^{-1}}\cdot -1t^{-2} \\ \quad \\ -\cfrac{1}{1+t^2}-\cfrac{1}{1+t^{-1}}\left( -\cfrac{1}{t^2}\right)\)

OpenStudy (jdoe0001):

on the second term, you'd do the chain-rule, is all

OpenStudy (marcelie):

hmm can you use qoutient rule

OpenStudy (jdoe0001):

well, you don't have a divisor or denominator, so hmm well.. on the second term? yes, you can, you'd end up in the same spot anyway

OpenStudy (marcelie):

oh hmmm okay so then

OpenStudy (marcelie):

(1/t^2) ^2 isnt that that 1/t^2

OpenStudy (jdoe0001):

hmm actually rats... yea, missed that part hmmm lemme redo it some

OpenStudy (marcelie):

ok lol

OpenStudy (marcelie):

brb..

OpenStudy (jdoe0001):

k

OpenStudy (jdoe0001):

\(\cfrac{d}{dx}[cot^{-1}(x)]=-\cfrac{1}{1+x^2}\qquad thus \\ \quad \\ cot^{-1}(t)+cot^{-1}\left( \frac{1}{t} \right)\implies cot^{-1}(t)+cot^{-1}\left( t^{-1} \right) \\ \quad \\ -\cfrac{1}{1+t^2}-\cfrac{1}{1+(t^{-1})^2}\cdot -1t^{-2}\implies -\cfrac{1}{1+t^2}-\cfrac{1}{1+\frac{1^2}{t^2}}\left( -\cfrac{1}{t^2} \right) \\ \quad \\ -\cfrac{1}{1+t^2}-\cfrac{1}{\frac{t^2+1}{t^2}}\left( -\cfrac{1}{t^2} \right)\implies -\cfrac{1}{1+t^2}-\cfrac{t^2}{t^2+1}\left( -\cfrac{1}{t^2} \right) \\ \quad \\ -\cfrac{1}{1+t^2}+\cfrac{\cancel{t^2}}{(t^2+1)\cancel{t^2}}\implies -\cfrac{1}{t^2+1}+\cfrac{1}{t^2+1}\implies \cfrac{\cancel{-1+1}}{t^2+1}\)

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